Charge sensors using inverted lateral bipolar junction transistors

ABSTRACT

A sensor includes a collector, an emitter and a base-region barrier formed as an inverted bipolar junction transistor having a base substrate forming a base electrode to activate the inverted bipolar junction transistor. A level surface is formed by the collector, the emitter and the base-region barrier opposite the base substrate such that when the level surface is exposed to charge, the charge is measured during operation of the bipolar junction transistor.

BACKGROUND

1. Technical Field

The present invention relates to semiconductor devices, and moreparticularly to charge sensors formed using inverted lateral bipolarjunction transistors.

2. Description of the Related Art

Conventionally, different types of sensors are fabricated for thedetection of different materials/substances. For example, Geigercounters are used to detect the radiation dose and provide a real-timebut semi-quantitative readout. Personal radiation dosimeters in the formof wearable badges are available but cannot provide real time readout.Bio-sensors, depending on the materials to detect, include quitedifferent structures, which very often require a certain amount of timefor readout due to the reaction/detection mechanism. Moreover, betterresolution/sensitivity requires longer processing time, which sometimesinvolves special instruments only available in laboratories, limitingthe portability of bio-sensors.

SUMMARY

A sensor includes a collector, an emitter and a base-region barrierformed as an inverted bipolar junction transistor having a basesubstrate forming a base electrode to activate the inverted bipolarjunction transistor. A level surface is formed by the collector, theemitter and the base-region barrier opposite the base substrate suchthat when the level surface is exposed to charge, the charge is measuredduring operation of the bipolar junction transistor.

Another sensor includes a collector, an emitter and a base-regionbarrier formed as an inverted bipolar junction transistor having a basesubstrate forming a base electrode to activate the inverted bipolarjunction transistor. A level surface is formed by the collector, theemitter and the base-region barrier opposite the base substrate suchthat when the level surface is exposed to charge, the charge is measuredduring operation of the bipolar junction transistor. A detection layeris disposed over the level surface and configured to interface with anitem to be measured such that interaction or contact with the substancegenerates charge measurable by the bipolar junction transistor.

Yet another sensor includes a base substrate including a monocrystallinesemiconductor material, a base-region barrier extending from the basesubstrate and including a monocrystalline structure having a same dopantconductivity as the base substrate, an emitter contacting a firstlateral side of the base-region barrier, and a collector contacting asecond lateral side opposite the emitter to form a bipolar junctiontransistor. The emitter and collector are spaced from the base substrateby a buried dielectric layer. The collector, the emitter and thebase-region barrier form a level surface opposite the base substrate. Adetection layer is disposed over the level surface such that when thedetection layer is exposed to charge, the charge is measured duringoperation of the bipolar junction transistor.

A method for forming a sensor includes forming a base-region barrier incontact with a base substrate, the base-region barrier including amonocrystalline semiconductor having a same dopant conductivity as thebase substrate; forming an emitter and a collector in contact with andon opposite sides of the base-region barrier to form a bipolar junctiontransistor; and planarizing the collector, the emitter and thebase-region barrier to form a level surface opposite the base substratesuch that when the level surface is exposed to charge, the charge ismeasured during operation of the bipolar junction transistor.

Another method for forming a sensor includes providing a semiconductoron insulator (SOI) substrate having a base substrate, a burieddielectric layer on the base substrate and a first semiconductor layeron the buried dielectric layer; patterning the first semiconductor layerto shape an emitter and a collector; etching through the burieddielectric layer to expose a portion of the base substrate; epitaxiallygrowing a base-region barrier extending from the portion of the basesubstrate to a position between the emitter and the collector, thebase-region barrier being in contact with the emitter and the collectorto form a bipolar junction transistor, the base-region barrier includinga same dopant conductivity as the base substrate; planarizing thecollector, the emitter and the base-region barrier to form a levelsurface opposite the base substrate such that when the level surface isexposed to charge, the charge is measured during operation of thebipolar junction transistor; and forming a detection layer on the levelsurface.

A sensing method includes providing a sensor having a collector, anemitter and a base-region barrier formed as an inverted bipolar junctiontransistor having a base substrate forming a base electrode to activatethe inverted bipolar junction transistor, and a level surface formed bythe collector, the emitter and the base-region barrier opposite the basesubstrate such that when the level surface is exposed to charge, thecharge is measured during operation of the bipolar junction transistor;accumulating charge at or near the level surface; and activating thebase substrate as a base electrode to enable the bipolar junctiontransistor to measure a dose or number of interactions which isproportional to the accumulated charge.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view of a sensor device including aninverted lateral bipolar junction transistor (ILBJT) in accordance withthe present principles;

FIG. 2 is a cross-sectional view of the sensor device including adetection layer on the ILBJT in accordance with the present principles;

FIG. 3 is a band diagram showing bands of the sensor of FIG. 1 whencharge (non-zero voltage) is applied to a top surface in accordance withthe present principles;

FIG. 4 is a band diagram showing bands of the sensor of FIG. 1 when nocharge (a zero voltage) is applied to a top surface in accordance withthe present principles;

FIG. 5 shows collector current (I_(C)) in A/micron versus base-emittervoltage (V_(BE)) in volts for different applied voltages (Vx) formeasuring accumulated charge in accordance with the present principles;

FIG. 6 shows barrier current (I_(B)) in A/micron versus base-emittervoltage (V_(BE)) in volts for different applied voltages (Vx) formeasuring accumulated charge in accordance with the present principles;

FIG. 7 shows collector current (I_(C)) in A/micron versus appliedvoltage (Vx) in volts for V_(BE)=0.4V for measuring accumulated charge(dose, radiation, etc.) in accordance with the present principles;

FIG. 8 is a cross-sectional view of a sensor device including adetection layer having a conversion layer and an accumulation layer formeasuring radiation (thermal neutrons) in accordance with the presentprinciples;

FIG. 9 is a cross-sectional view of a sensor device including adetection layer having a surface layer and an accumulation layer formeasuring chemical bonds (bio-materials or inorganic materials) inaccordance with the present principles;

FIGS. 10A-10E show cross-sectional views of a method for forming asensor in accordance with one illustrative embodiment;

FIG. 11 is a block/flow diagram showing other methods for fabricating asensor in accordance with illustrative embodiments; and

FIG. 12 is a block/flow diagram showing a method for employing a sensorin accordance with illustrative embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present principles provide a smart charge sensor fabricated with aninverted lateral semiconductor-on-insulator (SOI) Bipolar JunctionTransistor (BJT). The smart charge sensor may function as a radiationdosimeter, a bio-sensor, or any other detection device with properengineering of detection layers that can be independently placed on topof the sensor. The sensor exhibits high sensitivity and long-term chargeretention to enable long-term tracking. The smart sensor can be enabledfor detection of radiation, biological entities and chemical entitieswith appropriate structure/material engineering. The structure of thesmart sensor is preferably a Si-based device built on the invertedlateral SOI bipolar junction transistor (BJT) and its detectionmechanism is charge detection, which can be provide measurements inreal-time by measuring the charge.

In comparison to both fully-depleted silicon-on-insulator (FDSOI) metaloxide semiconductor filed effect transistors (MOSFET) and its bulkcounterparts, the inverted lateral SOI BJT charge sensor, in accordancewith the present principles, has at least the following advantages. Thesensor has ideal 60 mV/decade of I_(C)-V_(BE) (collectorcurrent-base-emitter voltage) characteristics, versus >60 mV/decade ofI_(D)-Vgs (drain current-gate-source voltage) characteristics of othertechnologies. The present sensors are not limited by the thickness of aburied oxide layer (BOX) or SOI substrate. FDSOI MOSFETs require a thinSOI substrate (e.g., less than 40 nm), which needs to be fully depletedin use, implying a potential contact resistance penalty. Also, thesub-threshold slope of the I_(D)-Vgs characteristics for the MOSFET isusually >60 mV/decade. These sub-threshold characteristics (thresholdvoltage, Vt) may deviate from the linear dependence of radiation doseespecially at extremely high dose. A sensing layer for the presentsensor can be readily custom engineered for a particular application.Good charge retention is rendered by using a dielectric, e.g., silicondioxide, as a sensing layer for the present sensors.

It is to be understood that the present invention will be described interms of a given illustrative device architecture having an invertedlateral SOI or SOI-like BJT design; however, other architectures,structures, substrate materials and process features and steps may bevaried within the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

A design for an integrated circuit chip in accordance with the presentprinciples may be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer may transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

Sensors in accordance with the present principles may be embedded incell phones, music players, satellite positioning devices, or even builtinto credit cards, driver's licenses, etc. In one application, a presentsensor may be employed by first responders to provide a reading devicethat would download integrated doses of materials so that treatmentdecisions could be made quickly. Other applications are alsocontemplated.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a charge sensor 100 (e.g.,an inverted lateral bipolar junction transistor (ILBJT)) is shown inaccordance with one embodiment. In this embodiment, the charge sensor100 does not include a detection layer over a top surface 102. Thecharge sensor 100 may be formed using a semiconductor-on-insulator (SOI)substrate 104, although other substrates and bulk materials may beemployed to form the same structure. The sensor 100 includes a basesubstrate 106 having a monocrystalline structure. The base substrate 106may include silicon, germanium, SiGe, GaAs, or any other semiconductormaterial. The base substrate 106 functions as a base electrode (henceinverted since the base electrode is on the bottom of the device). Thebase substrate 106 is coupled to a separately formed (grown) base-regionbarrier 108 which is the intrinsic base (or simply called the base) ofthe ILBJT. Base-region barrier 108 is preferably grown from the basesubstrate 106 and includes a monocrystalline or crystalline structurehaving the same materials as the base substrate 106.

A buried dielectric layer 110 separates the base substrate 106 from anemitter 112 and a collector 114. The buried dielectric layer 110 mayinclude oxide (e.g., silicon dioxide) although other dielectricmaterials are contemplated. The emitter 112 and collector 114 may beformed (patterned and doped) from a thin semiconductor layer 118 (e.g.,from the SOI structure). The emitter 112 and collector 114 may includesilicon, germanium, SiGe, GaAs, etc. The sensor 100 may includedifferent conductivities and dopant types. In one embodiment, theemitter 112 and collector 114 are n+ doped while the base substrate 106and the base-region barrier 108 are p doped. This forms an NPN bipolarjunction transistor. In other embodiments, a PNP bipolar junctiontransistor may be employed.

The operation of the sensor 100 provides current injected from the n+emitter 112 (E), across the base-region barrier (B) 108 to reach the n+collector (C) 114. This charge flows upon activation of the basesubstrate 106. Activation of the base substrate 106 may include applyinga voltage to the entire base substrate 106 or the base substrate may beisolated into sections and respective sections may be activated bydedicated circuits or connections (not shown). The activation voltage isa threshold voltage that permits charge to flow across the base-regionbarrier 108 from emitter 112 to collector 114. While the sensor 100 maybe employed in this form, preferred embodiments include a detectionlayer interface and/or an accumulation layer.

The emitter 112, collector 114 and base-region barrier 108 form a levelsurface 102. The surface 102 is preferably planar so that charge willevenly be distributed over the surface 102. In other designs, differentsurface shapes may be employed to provide different functionality, andcause charge build-up/accumulation at pre-determined locations on thesurface of the sensor 100.

Referring to FIG. 2, a detection layer 120 is formed over a surface ofthe emitter 112, base-region barrier 108 and collector 114. Thedetection layer 120 is configured to interact with, react with orotherwise interface with radiation, chemicals, mechanical elements,bio-matter, etc. The detection layer 120 is configured to cause thegeneration of charge that affects operation of the sensor 100 so that ameasurement of charge can be made.

In the embodiment of FIG. 1, no detection layer 120 is employed. Thispermits the measurement of induced charge or other charge that comes incontact with a top surface of the sensor 100 (e.g., an aqueous solutionof ions, etc.). In the embodiment of FIG. 2, the detection layer 120acts as an interface with the material or materials that are to bemeasured. In some embodiments, the detection layer 120 generates oraccumulates measurable charge as a result of its interaction with theitem or material(s) to be measured. During operation, charge present ator near a top layer of the sensor 100 causes depletion in thebase-region barrier 108 at or near the surface 102. A reading of thisaccumulated charge can be performed by activating the sensor 100 byenabling the base electrode (base substrate 106) to permit the sensor100 to operate (cause current flow).

Referring to FIG. 3, a band diagram is illustratively shown for thesensor 100. The band diagram shows the valence band edge E_(v) and theconduction band edge E_(c) versus a spatial dimension. A Fermi level(E_(F)) is indicated in the diagram. If there is positive charge (eitherthrough trapping or surface functionalization) in the detection layer120 (or at/through the top surface of the sensor 100), the lateral BJTresponds as if a positive voltage (Vx>0) is applied to the top of theinverted lateral SOI BJT (sensor 100) (e.g., a NPN device in this case).This causes depletion in the base-region barrier 108 near the surface(102). The barrier is lowered due to the depletion, leading to anincrease in collector current (I_(C)).

Referring to FIG. 4, another band diagram is illustratively shown forthe sensor 100 when (Vx=0). If there is no net charge in the detectionlayer 120 (or through the top surface of the sensor 100), the lateralBJT responds as if no voltage is applied to the top of the invertedlateral SOI BJT (sensor 100) (e.g., a NPN device in this case). TheILBJT operates normally without any change in collector current.

Referring to FIG. 5, plots showing collector current (I_(C)) (inA/micron) at base-emitter voltage (V_(BE)) of 0.4V for varying Vx (Vx=0,5, . . . , 20V) are illustratively depicted. The plots are generatedusing a buried oxide layer 140 nm in thickness and a silicon layerthickness for the collector and emitter of 50 nm. Also, the voltage frombase to collector (V_(BC)) was zero.

Referring to FIG. 6, plots showing base current (I_(B)) (in A/micron)versus base-emitter voltage (V_(BE)) (in volts) for varying Vx (Vx=0, 5,. . . , 20V) are illustratively depicted. The plots are generated usingthe buried oxide layer 140 nm in thickness and a silicon layer thicknessfor the collector and emitter of 50 nm. Also, the voltage from base tocollector (V_(BC)) was zero.

Data of I_(C) and I_(B) shown in FIGS. 5 and 6 depicts modulation(increased Vx), which simulates accumulated charge in the detectionlayer 120. Note that the modulation of I_(C) and I_(B) due to the chargeis similar in shape in both FIGS. 5 and 6.

Referring to FIG. 7, data point plots showing collector current (I_(C))(in A/micron) versus Vx (in volts), varying as 0, 5, . . . , 20V, areillustratively depicted. The plots are generated using a buried oxidelayer 140 nm in thickness and a silicon layer thickness for thecollector and emitter of 50 nm. Also, the voltage from base to collector(V_(BC)) was zero, and V_(BE) was 0.4V. The change of I_(C) as afunction of Vx (from oxide charge) at V_(BE)=0.4V is plotted and showsan exponential increase in I_(C) with Vx. This exponential dependence ofI_(C) on Vx makes the sensor 100 (e.g., an inverted lateral SOI BJT)more suitable than MOSFETs, which provide a linear change of thresholdvoltage with oxide charge for charge detection. The present embodimentsprovide the advantage of the 60 mV/decade I_(C)-V_(BE) characteristicsas opposed to >60 mV/decade for I_(d)-V_(gs) using a MOSFET. Suchadvantages permit increased sensitivity and provide more reliablereadings without the physical limitations of fully depleted MOSFETs(e.g., limitations of silicon thickness, etc.).

Referring to FIG. 8, one embodiment of the sensor 100 includes aradiation dosimeter 200. The dosimeter 200 includes a detection layer120 that can be configured as an interface to provide charge to besensed. The dosimeter 200 may be adapted to make measurements of chargedor other emitted particles. Since the effect of Vx>0 is equivalent topositive charge in the detection layer 120, ionizing radiation creates asimilar modulation of I_(C) as described above. Therefore, the invertedlateral SOI BJT can be utilized as the radiation dosimeter 200 bymeasuring the change in its I_(C) as a function of radiation dose.

In the embodiment of FIG. 8, the dosimeter 200 includes an invertedlateral SOI BJT, which functions to measure thermal neutrons (n).Thermal neutrons are neutrons having energy capable of causing a nuclearfission reaction. Detection of these neutrons can be useful fordetecting nuclear events (e.g., the event of nuclear plant meltdown orradiological-dispersal bomb detonation) or for monitoring operations orsafety in nuclear facilities.

A thermal neutron conversion layer 202 is incorporated into thedetection layer 120. The conversion layer 202 is preferably formed overa charge accumulation layer 204, which is preferably a dielectric layeror stack of layers. In one embodiment, the charge accumulation layer 204includes an oxide layer (e.g., SiO₂) although other dielectric materialsmay also be employed, e.g., silicon nitride, etc. Incoming thermalneutrons will react with the material of the conversion layer 202 andgenerate ionizing particles, e.g., alpha particles (α) (He²⁺), protons(p), X-rays (e⁻), gamma (γ) rays, beta particles (β), etc. which createpositive charge 206 that is eventually trapped in the accumulation layer204.

The thermal neutron conversion layer 202 may be comprised of a singlematerial, multiple materials or layers of materials. The materials areconfigured and dimensioned (e.g., thicknesses) to cause an appropriatereaction for generating charge to be accumulated in the accumulationlayer 204. TABLE 1 shows some illustrative materials, the reactions ofthe materials with thermal neutrons and some of the materials'characteristics. The materials that may be employed in the thermalneutron conversion layer 202 have an isotopic abundance for the isotopeof the material which is listed in TABLE 1. The particles emitted by thereaction and the respective energy of the reaction are also shown. Thereactions shown in TABLE 1 all have large cross sections for thermalneutron capture but the outgoing particles are emitted at relatively lowenergy. The range of these ions in silicon (e.g., penetration depth) asa function of their energy results in most of the outgoing chargedparticles being absorbed in a few micrometers in silicon.

These outgoing charged particles would stop completely if directed ontothe thick silicon substrate below the sensor device (base substrate).Notwithstanding this, additional shielding or moderating materials maybe employed to ensure the outgoing charged particles are completelycontained. The additional shielding or moderating materials may beconfigured to support omnidirectional thermal neutron measurements. Thedosimeter would detect thermal neutrons in any orientation, since thethermal neutrons would easily penetrate the top or sides of thedosimeter.

TABLE 1 Isotopic Emitted Emitted Cross abundance particle and particleand Section Reaction (%) energy energy (B) ¹⁰B (n, α) 19.8$\frac{{\,^{7}{Li}},0.84}{MeV}$ $\frac{\alpha,1.47}{MeV}$ 3840 ⁶Li (n,α) 7.4 $\frac{{\,^{3}H},2.73}{MeV}$ $\frac{\alpha,2.05}{MeV}$ 940 ³He(n, p) 1.4E−4 $\frac{{\,^{3}H},0.19}{MeV}$ p, 0.57 MeV 5330 ¹⁵⁷Gd (n,e⁻) 15.7 e⁻, 72 keV 255,000

Referring to FIG. 9, another embodiment of the sensor 100 includes abio-sensor 300. The bio-sensor 300 includes a detection layer 120 thatcan be configured as an interface to provide charge to be sensed fromcontact or interaction with bio-materials. The bio-sensor 300 includesthe inverted lateral SOI BJT structure as described above with adetection surface 302 for sensing of bio-molecules, such as proteins,viruses, ions, etc. from solution or in air. As before, I_(C) would bemonitored as the sensing signal at a fixed V_(BE).

The surface 302 may be distributed over an accumulation layer 204. Thesurface 302 would include or be modified so as to specifically bind amolecule or compound under study. For example, to detect a specificprotein (such as, e.g., streptavidin), the surface 302 would be coatedwith a corresponding antibody (such as, e.g., biotin) that specificallybinds the proteins of interest. Since most bio-molecules are charged,bound bio-molecules would create charge on the surface 302 with aconcomitant change in the voltage Vx. This bio-molecule induced changein Vx would cause the sensing signal I_(C) to exponentially vary asshown in FIG. 5. Hence, the bio-sensor 300 detects bio-molecules withhigh sensitivity at low sensing voltages V_(BE).

Referring to FIGS. 10A-10E, a method for forming a sensor 310 is shownin accordance with one illustrative embodiment. In FIG. 10A, asemiconductor material 320 is formed on or grown on a substrate 322. Inone embodiment, the semiconductor layer 320 is p doped and the substrateis p+ doped. In other embodiments, the semiconductor layer 320 is ndoped and the substrate is n+ doped. The semiconductor layer 320 andsubstrate 322 may include monocrystalline silicon or other materialsdescribed for base-region barrier 108 and base substrate 106,respectively.

In FIG. 10B, the semiconductor layer 320 is patterned and etched orotherwise shaped, as needed, for a base-region barrier 324. A dielectriclayer is deposited and planarized to the base-region barrier 324 to formdielectric trench regions 326. The dielectric trench regions 326 mayinclude an oxide or other suitable material.

In FIG. 10C, the dielectric trench regions 326 are masked and etched(e.g., reactive ion etching) to form trenches 330. The trenches 330define regions for the formation of emitter and collector regions. InFIG. 10D, a doped polysilicon layer 332 is deposited in the trenches. Inthis example, the polysilicon is n+ doped; however, if the base region324 and the substrate 322 are n-doped, the polysilicon is p+ doped.

In FIG. 10E, the polysilicon 332 is planarized to form a level surface(from the barrier 324, an emitter 336 and a collector 338) for the ILBJTdevice 310. A detection layer 334 may be deposited over the base regionbarrier 324, the emitter 336 and the collector 338. Additional stepsinclude forming contacts and other metallizations to provide connectionsto the appropriate regions of the ILBJT 310.

Referring to FIGS. 11 and 12, aspects of the present invention aredescribed below with reference to flowchart illustrations and/or blockdiagrams of methods according to embodiments of the invention. Theflowchart and block diagrams in the FIGs. illustrate the architecture,functionality, and operation of possible implementations according tovarious embodiments of the present invention. It should also be notedthat, in some alternative implementations, the functions noted in theblocks may occur out of the order noted in the FIGs. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

Referring to FIG. 11, another method for forming a sensor isillustratively shown in accordance with exemplary embodiments. In block402, a substrate is provided. The substrate may include a semiconductoron insulator (SOI) substrate having a base substrate, a burieddielectric layer on the base substrate and a first or top semiconductorlayer on the buried dielectric layer. Other substrates and materials mayalso be employed to provide the structure described herein in accordancewith the present principles (FIG. 10A). In block 404, the firstsemiconductor layer is patterned to shape an emitter and a collector.The patterning may include etching the emitter and collector shapes inthe first semiconductor layer as well as etching through a portion ofthe buried dielectric layer. In block 406, the buried dielectric layeris etched to expose a portion of the base substrate. The etching mayremove a small portion of the base substrate as well to expose apristine area to grow a base-region barrier structure. Note that thebase substrate or portions thereof are connected to circuits, contacts,etc. to permit a voltage to be applied thereto to activate a resultantBJT device as will be described.

In block 408, a base-region barrier is epitaxially grown extending fromthe portion of the base substrate to a position between the emitter andthe collector. The base-region barrier is in contact with the emitterand the collector on opposite lateral sides to form a bipolar junctiontransistor. The barrier includes a same dopant conductivity as the basesubstrate. The barrier may be doped in-situ or after formation usingknown doping methods. The base substrate may be doped in advance as wellby known methods.

In block 420, the collector, the emitter and the base-region barrier areplanarized to form a level surface on top (e.g., opposite the basesubstrate) such that when the level surface is exposed to charge, thecharge is measured during operation of the bipolar junction transistor.Planarization may include chemical mechanical polishing (CMP) or otherprocesses.

In block 426, a detection layer may be formed on the level surface. Inblock 428, the detection layer may be formed from an accumulation layerand a conversion layer such that the conversion layer turns interactionswith the conversion layer into charge which is accumulated in theaccumulation layer. In block 430, the conversion layer may be configuredto convert incident radiation into charge; the radiation may include atleast one of alpha particles, beta particles, protons, neutrons,electromagnetic radiation, etc.

In block 432, the detection layer may be formed from an accumulationlayer and a detection surface such that the detection surface isconfigured to bond with a material to provide charge which isaccumulated in the accumulation layer. In block 434, the detectionsurface may be configured to convert molecular bonds into charge. Themolecular bonds include at least one of bonds with proteins, viruses andions. The bonds may also include chemical bonds for inorganic compounds,other bio-materials and elements.

In block 440, the detection layer may be removed, e.g., by etching orother processing, and the detection layer may be restored, renewed orrepaired as needed. In addition the detection layer may be reconfiguredto permit sensing operations of different materials using the same basedevice (ILBJT). In other embodiments, a plurality of sensors may beemployed in an array to sense a same radiation, compound etc. ordifferent radiations, compounds, etc.

Referring to FIG. 12, a sensing method using the sensors in accordancewith the present principles is illustratively shown in accordance withexemplary embodiments. In block 502, a sensor is provided having acollector, an emitter and a base-region barrier formed as an invertedbipolar junction transistor and having a base substrate that forms abase electrode to activate the inverted bipolar junction transistor. Alevel surface is formed by the collector, the emitter and thebase-region barrier opposite the base substrate such that when the levelsurface is exposed to charge, the charge is measured during operation ofthe bipolar junction transistor. The sensor preferably includes adetection layer on the level surface.

The detection layer may include an accumulation layer and a conversionlayer such that the conversion layer turns interactions with theconversion layer into charge which is accumulated in the accumulationlayer. The conversion layer may be configured to convert incidentradiation into charge, the radiation including at least one of alphaparticles, beta particles, protons, neutrons, electromagnetic radiation,etc. The detection layer may include an accumulation layer and adetection surface such that the detection surface is configured to bondwith a material to provide charge which is accumulated in theaccumulation layer. The detection surface is configured to convertmolecular bonds into charge. The molecular bonds may include at leastone of bonds with proteins, viruses and ions. The bonds may also includechemical bonds for inorganic compounds or other bio-materials andelements.

In block 508, charge is accumulated at or near the level surface. Inblock 512, the base substrate is activated as a base electrode to enablethe bipolar junction transistor to measure a dose or number ofinteractions which is proportional to the accumulated charge.

In block 514, the dose or number of interactions is measured using atleast one of a collector current and a base current of the invertedbipolar junction transistor, which is proportional to accumulatedcharge. In one embodiment, an exponential relationship exists betweenthe at least one of the collector current and the base current and avoltage caused by the accumulated charge. In block 516, the detectionlayer may be replaced or reconfigured, as needed.

Having described preferred embodiments for charge sensors using invertedlateral bipolar junction transistors (which are intended to beillustrative and not limiting), it is noted that modifications andvariations can be made by persons skilled in the art in light of theabove teachings. It is therefore to be understood that changes may bemade in the particular embodiments disclosed which are within the scopeof the invention as outlined by the appended claims. Having thusdescribed aspects of the invention, with the details and particularityrequired by the patent laws, what is claimed and desired protected byLetters Patent is set forth in the appended claims.

What is claimed is:
 1. A sensor, comprising: a collector, an emitter and a base-region barrier formed as an inverted bipolar junction transistor having a base substrate forming a base electrode to activate the inverted bipolar junction transistor; a level surface formed by the collector, the emitter and the base-region barrier opposite the base substrate such that when the level surface is exposed to charge, the charge is measured during operation of the bipolar junction transistor; and a detection layer directly on an entirety of the level surface.
 2. The sensor as recited in claim 1, wherein the base electrode is selectively activated to enable the inverted bipolar junction transistor to make a measurement.
 3. The sensor as recited in claim 1, wherein accumulated charge at or near the level surface affects a collector current of the inverted bipolar junction transistor.
 4. The sensor as recited in claim 3, wherein an exponential relationship exists between the collector current and a voltage caused by the accumulated charge.
 5. The sensor as recited in claim 1, wherein an accumulated charge in the detection layer is proportional to a dose or number of interactions with material to be measured at the detection layer.
 6. The sensor as recited in claim 5, wherein the detection layer includes an accumulation layer and a conversion layer such that the conversion layer turns interactions therewith into charge which is accumulated in the accumulation layer.
 7. The sensor as recited in claim 6, wherein the conversion layer converts incident radiation into charge, the radiation including at least one of alpha particles, beta particles, protons, neutrons, and electromagnetic radiation.
 8. A sensor, comprising: a collector, an emitter and a base-region barrier formed as an inverted bipolar junction transistor having a base substrate forming a base electrode to activate the inverted bipolar junction; a level surface formed by the collector, the emitter and the base-region barrier opposite the base substrate such that when the level surface is exposed to charge, the charge is measured during operation of the bipolar junction transistor; and a detection layer disposed over an entirety of the level surface and configured to interface with an item to be measured such that interaction or contact with the substance generates the charge measurable by the bipolar junction transistor.
 9. The sensor as recited in claim 8, wherein the base electrode is selectively activated to enable the inverted bipolar junction transistor to make a measurement.
 10. The sensor as recited in claim 8, wherein accumulated charge at or near the level surface affects a collector current of the inverted bipolar junction transistor.
 11. The sensor as recited in claim 10, wherein an exponential relationship exists between the collector current and a voltage caused by the accumulated charge.
 12. The sensor as recited in claim 8, wherein the detection layer stores an accumulated charge, which is proportional to a dose or number of interactions with the item to be measured.
 13. The sensor as recited in claim 8, wherein the detection layer includes an accumulation layer and a conversion layer such that the conversion layer turns interactions therewith into charge which is accumulated in the accumulation layer.
 14. The sensor as recited in claim 13, wherein the conversion layer converts incident radiation into charge, the radiation including at least one of alpha particles, beta particles, protons, neutrons, and electromagnetic radiation.
 15. A sensor, comprising: a base substrate including a monocrystalline semiconductor material; a base-region barrier extending from the base substrate and including a monocrystalline structure having a same dopant conductivity as the base substrate; an emitter contacting a first lateral side of the base-region barrier; and a collector contacting a second lateral side opposite the emitter to form a bipolar junction transistor, the emitter and collector being spaced from the base substrate by a buried dielectric layer, the collector, the emitter and the base-region barrier forming a level surface opposite the base substrate; and a detection layer disposed over an entirety of the level surface such that when the detection layer is exposed to charge, the charge is measured during operation of the bipolar junction transistor.
 16. The sensor as recited in claim 15, wherein the base substrate forms a base electrode to selectively enable operation of the inverted bipolar junction transistor and accumulated charge at or near the level surface affects a collector current of the inverted bipolar junction transistor and further wherein an exponential relationship exists between the collector current and a voltage caused by the accumulated charge.
 17. The sensor as recited in claim 15, wherein the detection layer includes an accumulation layer and a conversion layer such that the conversion layer turns interactions therewith into charge which is accumulated in the accumulation layer, wherein the conversion layer converts incident radiation into charge, the radiation including at least one of alpha particles, beta particles, protons, neutrons, and electromagnetic radiation. 